1. Field of the Invention
The present invention relates to a method for sorting a reusable nonaqueous electrolyte secondary battery from spent nonaqueous electrolyte secondary batteries. The present application claims priority to Japanese Patent Application No. 2015-153689 filed on Aug. 3, 2015, the entire contents of which are hereby incorporated by reference.
2. Description of the Related Art
Nonaqueous electrolyte secondary batteries such as lithium ion secondary batteries have been used in recent years as the so-called portable power sources for personal computers, portable terminals, and the like, and as drive power sources for vehicles because they are lighter in weight and higher in energy density than presently available batteries. In particular, lightweight lithium ion secondary batteries that can provide a high energy density are expected to be hereinafter increasingly popular as high-output drive power sources for vehicles such as electric vehicles (EV), hybrid vehicles (HV), and plug-in hybrid vehicles (PHV).
When nonaqueous electrolyte secondary batteries are used, for example, as a high-output drive power source for a vehicle, they are used as a battery pack in which a plurality of nonaqueous electrolyte secondary batteries (unit batteries) are electrically connected to each other. For example, when a service life of a battery pack, for example, in a vehicle, has been reached, the battery pack needs to be replaced. Therefore, diagnosis is performed to determine whether or not the service life of the battery pack which has been used is reached. As such a diagnosis method, WO 2012/049852 discloses a diagnosis method relating to reuse of a battery pack, the method including a step of dividing a plurality of unit batteries in the battery pack into a plurality of blocks and calculating the internal resistance of each block, and a step of specifying the highest internal resistance, among the internal resistances of the blocks, as a determination indicator relating to the reuse of the battery pack.